The present invention relates to the diagnosis of link failures in a network.
There are various standard protocols for operation of a network. We will be describing an arrangement which uses Ethernet in the gigabit range (protocol IEEE 803.2—1000BASE-X), although the principle may be applied to other protocols.
As is well known, 1000BASE-X networks operate on optical fibre full duplex links. Under the IEEE Standard 802.3, two devices when initiating communication with one another across a network (“handshaking”) allow the devices to exchange information about their abilities. At its simplest, it is necessary for the two devices to be aware of the level (eg speed) of protocol at which they each operate so as to chose the highest speed protocol common to each of them This process which involves the exchange of “pages” of information with each other, and which is referred to as auto-negotiation thus provides automatic speed matching for devices which are capable of operating at a variety of speeds in accordance with a variety of protocols.
Link failures may happen in a network at any time and various proposals have been made to determine the cause of such link failures. However, there is a particular problem in a special circumstance as follows. When a manufacturer designs a new component to operate in such a network in accordance with a pre-determined protocol, it is sometimes found that there are problems whereby the new component does not link properly with the reminder of the network. Two matters can make identification of a problem more difficult. Firstly, device never connects properly and secondly the protocol is a new one.
The difficulty in this particular case is that one has little experience to determine what the problem might be, particularly if the link does not start or simply goes down.
Examples of link failure are:                loss of light;        bit/word alignment failure;        loss of synchronisation during auto-negotiation;        auto-negotiation protocol hang during base page exchange;        auto-negotiation protocol hang during next page exchange;        auto-negotiation protocol (repeated) restart due to link partner initiating a “break link”.        
In copper or optical fibre links, the management interface to the PHY device (physical layer) provides minimal visibility of link failures. So far as the interface is concerned, the link is either “up” or “down” or “was down but has since come up”. Testing one manufacturer's products ability to co-operate with another competitor's products using the relevant protocol can render it difficult to isolate faults when failure occurs.
There are networks analysers which can be purchased, which offer link diagnostic capabilities, but such devices do not usually exist in the early stages of a new protocol, for example gigabit Ethernet. Also such devices do not necessarily reflect the true state of the link nodes. There is a particular problem in understanding auto-negotiation breakdown.